1. Field of the Invention
The present invention relates to very small-scale ground occurrence detection equipment, and more particularly to very small-scale ground occurrence detection equipment capable of detecting very small-scale grounding in a distribution power system while maintaining the line energized.
2. Description of Related Art
When deterioration occurs in any equipment or materials in a distribution line, it is required to quickly identify, out of many electric poles, the equipment or materials thereof where it is actually occurring, thereby to remedy it.
For this purpose, deterioration inspecting methods have been proposed, for example, in "Electric Review" January, '90, p 46, "Electric Joint Research", vol. 42, no. 1, p 23 and "Japan Electric Association", 68th General Session, Research Report p. 114-115, in which the distribution line is divided into a plurality of zones by switches and the zones are successively inspected for identifying the defective zone by interrupting a power supply to the zone to be inspected and applying a high tension pulse between the zone and the ground.
Further, there are proposed detection methods in "Electric Joint Research", vol. 42, no. 1, p-35 or in "Electric Joint Research", vol. 43, no. 2, p-204 to 205 for detecting ultrasonic noises or high frequency noises occurring from a discharge-type deterioration point using microphone or antenna.
The former methods hereinabove are implemented on the premise that the defective line must be specified in advance. In addition, the detection of the defective zone must be performed under outage of the power, resulting in inconvenience of the users.
The latter methods hereinabove are implemented under live wire condition thereby eliminating the inconvenience of the users due to outage of power imposed at any time when the inspection is required. However, they are effective only when the discharge-type ground fault phenomena in the degraded equipment or materials continue under a normal line voltage. Namely, according to these methods, the detection of deterioration is possible only when the deterioration has progressed to such an extent as to cause discharge phenomena to occur under the normal line voltage. Thus, the methods are contrary to the object of the present invention to detect any deterioration in equipment and materials at its earlier stage of occurrence.